This invention relates generally to a semiconductor device assembly, and in particular, relates to a connection of integrated circuit (IC) chip or chips to substrate circuitry, printed circuit board, and interconnect components.
Recent developments of semiconductor packaging suggest an increasingly critical role of the technology. New demands are coming from requirements for more leads per chip and hence smaller input/output terminal pad pitch, shrinking die and package footprints, and higher operational frequencies that generate more heat, thus requiring advanced heat dissipation designs. All of these considerations must be met and, as usual, placed in addition to the cost that packaging adds to the overall semiconductor manufacturing costs.
Conventionally, there are three predominant chip-level connection technologies in use for integrated circuits, namely wire bonding, tape automated bonding (TAB) and flip chip (FC) to electrically or mechanically connect integrated circuits to leadframe or substrate circuitry. Wire bonding has been the far most broadly applied technique in the semiconductor industry because of its maturity and cost effectiveness. However, this process can be performed only one wire bond at a time between the semiconductor chip""s bonding pads and the appropriate interconnect points. Furthermore, because of the ever increasing operational frequency of the device, the length of the interconnects needs to be shorter to minimize inductive noise in power and ground, and also to minimize crosstalk between the signal leads. An example of such a method is disclosed in U.S. Pat. No. 5,397,921 issued to Karnezos.
Flip chip technology is characterized by mounting of the unpackaged semiconductor chip with the active side facing down to an interconnect substrate through contact anchors such as solder, gold or organic conductive adhesive bumps. The major advantage of flip chip technology is the short interconnects which can, therefore, handle high speed or high frequency signals. There are essentially no parasitic elements, such as inductance. Not only is the signal propagation delay slashed, but much of the waveform distortion is also eliminated. Flip chip also allows an array interconnecting layout that provides more I/O than a perimeter interconnect with the same die size. Furthermore, it requires minimal mounting area and weight which results in overall cost saving since no extra packaging and less circuit board space is used. An example of such a method is disclosed in U.S. Pat. No. 5,261,593 issued to Casson et al.
While flip chip technology has tremendous advantages over wire bonding, its cost and technical limitations are significant. First of all, prior art flip chip technology must confront the challenge of having to form protruded contact anchors or bumps to serve as electrical connections between the integrated circuit chip and substrate circuitry. Examples of such an approach are disclosed in U.S. Pat. No. 5,803,340 issued to Yeh et al. and U.S. Pat. No. 5,736,456 issued to Akram. These approaches typically include a very costly vacuum process to deposit an intermediate under-bump layer that serves as an adhesive and diffusion barrier. This barrier layer is typically composed of a film stack that can be in the structure of chromium/copper/gold. Bumping materials such as solder are subsequently deposited onto this intermediate layer through evaporation, sputtering, electroplating, solder jetting or paste printing methods followed by a reflow step to form the solder contacts. Although evaporation and sputtering can potentially offer high density bumps, these processes need very tight control and normally result in poor yield. As a result, a conventional flip chip assembly is not only very costly but also suffers from very serious reliability problems and a high fatality ratio.
Techniques for fabricating the intermediate under-bump barrier layer as well as the bump material utilizing electroless plating are also known in the prior art. An example of such a method is described in the U.S. Pat. No. 5,583,073 issued to Lin et al. Although the electroless technique provides an economical, simple and effective method for providing an under-bump barrier layer, contacting material such as solder or adhesive is still required for assembling. Solder dipping or screen printing of solder paste onto these bumps has been explored but has been met with very limited success due to lack of solder bridging control and non-uniform deposition of solder on the metal bumps. This process also suffers from poor process control as input/output terminal pad spacing gets smaller.
In view of the limitations of currently available integrated circuit assembling methods, a high performance, reliable and economical device and method that can effectively interconnect integrated circuits to the external circuitry would be greatly desirable.
It is therefore an object of the present invention to provide a flip chip assembly to address high density, low cost and high performance requirements of semiconductor packaging. The device and method of the present invention involve the bonding of substrate circuitry to a semiconductor device through the reflowing of pre-deposited solder to connect via apertures or holes of the substrate to terminal pads of the semiconductor device without the need for conventional bumps, bonding wire, or other media.
More specifically, the present invention relates to a chip assembly that includes a single or multi-layered substrate of which circuitry is connected to the input/output terminal pads of the IC chip through solder reflow in the via holes. The solder deposition techniques include electrolytic plating, electroless (chemical) plating, wave soldering, meniscus coating and solder printing.
In summary, using soldering material directly reflowed between a via hole and a terminal pad can effectively connect an IC chip and dielectric substrate circuitry without external bumps or wires. This approach allows a reliable, low profile, high performance and low cost assembly to be achieved. In particular, a small via hole formed by laser drilling or other techniques allows a very fine pitch terminal pad to be interconnected, which can significantly enhance the capability of packaging future high I/O semiconductor chips.